344 



THE FOODS WE EAT 



What is "dry ice"? 



Is it really dry ? What 



are the advantages of 



dry ice ? 



being about 140 F. colder than ice itself, and hence a small 

 cube of it will do the work of a much larger piece of ice. 

 In addition, dry ice lasts longer than ordinary ice. A 

 forty-pound piece uncovered in a store 

 window during the summer would last 

 about twenty-four hours. Dry ice 

 evaporates slowly without leaving any 

 liquid behind to rust or corrode the 

 container. At present, it is used hi 

 the refrigeration of perishable foods 

 in transit, and particularly for the 

 transportation of small packages of 

 ice cream. 



The Iceless Refrigerator. In hot 

 countries, one finds porous skins and 

 unglazed earthenware vessels filled 

 with water hanging in a breeze in the 

 shade. The natives have learned that the water gets 

 cooler when so treated, though they do not understand 

 why. When water evaporates, it absorbs heat. If you 

 wet your hand and swing it in the air, it feels cooler. 

 This is due to the absorption of heat during evaporation. 

 Thermos Bottle. The thermos bottle is really a double- 

 walled bottle, or one bottle inside of another with a 

 vacuum between them. A vacuum is a better insulator 

 than air. The inside walls of the bottles surrounding 

 the vacuum are mirrors which reflect the heat rays and 

 prevent their passage across the vacuum. 



A Clean Kitchen Necessary. Since foods are handled 

 in the kitchen, it goes without saying that a clean kitchen 

 will aid greatly in preventing the spoiling of foods. All 

 surfaces in the kitchen should be washed frequently. 

 Wooden surfaces, especially when they become greasy, 

 make excellent dwelling places for bacteria. For this 

 reason tiled surfaces are more hygienic than wood. Re- 



